Silicon photonics based optical network

ABSTRACT

Various implementations of network devices disclosed herein provide a method routing a data packet in an optical domain, the data packet including a first component or header and second component or routing information, stripping the first component or header from the data packet using a silicon photonic component, processing the first component or header in an electrical domain, and communicating the data packet without the first component or header to an optical delay line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application based on and claimspriority to U.S. Provisional Application Ser. No. 62/549,107 entitled“Silicon Photonics Based Storage Network” filed on Aug. 23, 2017, whichis incorporated herein by reference in its entirety.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Otherfeatures, details, utilities, and advantages of the claimed subjectmatter will be apparent from the following, more particular writtenDetailed Description of various implementations as further illustratedin the accompanying drawings and defined in the appended claims.

Various implementations of storage devices disclosed herein provide amethod routing a data packet in an optical domain, the data packetincluding a header including routing information, stripping the headerfrom the data packet using a silicon photonic component, processing theheader in electrical domain, and communicating the data packet withoutthe header to an optical delay line.

These and various other features and advantages will be apparent from areading of the following Detailed Description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

A further understanding of the nature and advantages of the presenttechnology may be realized by reference to the figures, which aredescribed in the remaining portion of the specification.

FIG. 1 illustrates an example communication network with a number ofwaveguides, each of the waveguides configured to communicate opticalsignals over a number of wavelengths.

FIG. 2 illustrates an example block diagram of a system to increase theinput/output (I/O) capacity of a storage system controller or a systemon chip (SOC) by I/O expansion using silicon photonics.

FIG. 3 illustrates example operations for efficiently routing orswitching optical signals for data-centric datacenter architectures.

FIG. 4 illustrates example operations for arbitrating access to a set ofwavelengths in a wavelength-identified optical ASIC interconnectnetwork.

FIG. 5 illustrates an example communication network using MRRs withselective wavelength keying.

FIG. 6 illustrates an example graph illustrating relation betweenresonant wavelength of MRRs and heater power applied to the MRRs.

FIG. 7 illustrates an example communication network with optical delaylines for silicon photonics routing.

DETAILED DESCRIPTION

Currently high-performance computing systems composed of many ASICdevices utilize copper interconnect to allow the devices to communicate.This interconnect creates bandwidth bottlenecks between the devices thatcan be the limiting factor in a system's performance. New advances inmicro-ring resonators (MRRs) promise increased chip-to-chipcommunication bandwidth and latency by utilizing optical interconnectrather than physical interconnect. This presents some new challenges tobe solved of how to efficiently route information in an opticalinterconnect network with minimal latency. An implementation proposedherein solves this problem by identifying destination identifications(IDs) by assigning each destination a specific set of wavelengths sothat any source can have its transmission routed to the finaldestination just by transmitting on a specific set of wavelengths.

In a system such as this there is a substantial amount of interconnectbandwidth as compared to copper since transmissions to differentdestinations can be simultaneously sent on the same optical element.However, when multiple sources all try to transmit to the samedestination, at some points in the interconnect, those transmissions mayconflict with one another leading to loss of that transmission withoutan arbitration scheme.

FIG. 1 illustrates a communication network 100 with a number ofwaveguides, each of the waveguides configured to communicate opticalsignals over a number of wavelengths. Specifically, the communicationnetwork 100 includes an incoming waveguide 4102 that carries opticalsignals over a large number of different wavelengths. For example, theincoming waveguide 4102 may be carryings a large number of opticalsignals from a controller where each of these signals are to be directedto a different destination packages S₁, S₂, S₃, etc.

Silicon photonic components 4104, 4106 are configured in the vicinity ofthe waveguides 4102 and they resonate at given wavelengths such thatthey are able to alter the path of optical signals traveling on anincoming waveguide 4102 towards an outgoing waveguide 4108. In oneimplementation, the silicon photonic components 4104, 4106 areimplemented using ring resonators, such as micro ring resonators (MRRs).An MRR's wavelength can be changed (by heating it up or down) inapproximately 16 micro-second from one frequency to any otherfrequency/channel. Alternatively, the silicon photonic components 4104,4106 are implemented using Mach-Zehnder Interferometer (MZI) SiPhcomponent. In some alternative embodiments, the silicon photoniccomponent may be a magnetic ring resonator.

For example, a command may come in on wavelength λx at 4102 and thecommunication network 200 may need to respond to (forward) that commandon wavelength λy. Based on an incoming wavelength λx, the system knowsthe processor the command came from. Furthermore, based on thewavelength λy, the system may also know a package Si of NAND device thatthe command is directed to. In one implementation, when a read commandcomes in, the communication network 200 may have 10 micro-second beforedata starts coming in. Thus, the communication network 200 may have 10micro-second to determine which NAND drive the data is directed to.Thus, the communication network 200 has 10 micro-second to tune the MRR4104, 4106. This is of the order of the time it takes to tune the MRR(16 micro-second).

When a NAND controller managing the communication network 200 hasstaggered commands on wavelength 4104 coming in, if there are two MRRs4104 and 4106 to choose from, the system can tune one MRR 4014 whiletransmitting on the other wavelength. For example, the MRR 4104 may beconfigured to resonate at a wavelength λs_(1a) and the MRR may beconfigured to resonate at a wavelength λs_(1b). As a result, an opticalsignal traveling on the waveguide 1102 at the frequencies λs_(1a) andλs_(1b) are directed to the destination package S₁. In thisimplementation, tuning of the MRRs is happening in the electricaldomain.

FIG. 2 illustrates an example block diagram 200 of a system to increasethe input/output (I/O) capacity of a storage system controller or asystem on chip (SOC) by I/O expansion using silicon photonics.Specifically, the storage controller 202 is configured with a siliconphotonics transceiver 204 that converts one or more electrical domainsignals into optical signals. The optical signals are communicated overan optical network to various silicon photonic transceivers 206 that areconfigured with expanders 208. The silicon photonic transceivers 206convert the received optical signal into a signal in electrical domainand feed them into the expanders 208.

Each of the expanders are connected to multiple NANDs 210 to communicatethe electrical domain signals thereto. Datacenters are moving towarddata-centric architectures driven by the need for performance and energyefficiency. In data-centric architectures, large pools of memory areshared by pools of heterogeneous compute resources (CPU, GPU, TPU,FPGAs, etc). These architectures require and are enabled by low latency(<<100 ns) network fabrics for example using SiPh. Variousimplementations move to lower latency memory-semantics based fabrics(such as Omnipath, Gen-Z, etc.). These are still wire-based and havelower limits of latency and energy/bit due to RLC of wires.

Implementations disclosed herein use MRR based transceivers as well asrouting structures to make interconnect latency a function oflight-speed rather than RLC delays. Maximizes energy efficiency andminimizes latency by keeping data in the optical domain as much aspossible and switching back to the electrical domain only for computeand storage. Important because it enables any point to point latencywithin a datacenter to be close to speed-of-light delays. This in turnenables data or memory-centric architectures in datacenters.

For example, in an implementation disclosed in FIG. 3, an operation 302integrates SiPh transceivers in controller silicon to implement thephysical layer of memory and compute interfaces (Gen-Z, OmniPath). Thesetransceivers may be integrated into the memory controller SoC (e.g. SSD,or HDD) as well as in memory packages (NAND, SCM, HBM). An operation 304routes optical signals through the SiPh transceivers.

An arbitration scheme disclosed herein allows for conflicts to beresolved by a method disclosed by the operations 400 illustrated in FIG.4. An operation 102 encodes the sources ID along with a validation code(e.g. a cyclic redundancy check “CRC”) in the transmission the sourcesends to the destination. An operation 104 sends an acknowledgementtransmission sent from the destination to the source to validate that avalid transmission has been received by the destination (i.e. it hasn'tbeen corrupted by other transmissions).

A pseudo-random or source ID-sensitive retry protocol 108 is performedwhere the source retransmits its transmission if it doesn't not receivean acknowledge signal within an implementation-specific period of timeat 106. The time between retries is either randomized or is affected bythe source ID itself so that subsequent re-transmissions bynon-acknowledged sources have an increasing probability of a successfultransmission.

Memory controllers need to address an increasing number of memorydevices. These controller SoCs are pad limited when it comes toaddressing hundreds of memory devices (Flash, ReRAM, SCM, DRAM etc). Theuse of bus-expander silicon has been the typical approach in addressingthis challenge. The issue with this approach is that it uses long reach(often) parallel buses which require significant energy and are speedlimited.

An implementation disclosed herein exploits recent advancements insilicon photonic micro-ring resonator (MRR) based transceivers capableof being manufactured in standard CMOS processes and hencemonolithically integrate-able into memory controller silicon.Interconnects using this technology have latencies dependent on speed oflight and are not subject to the distance dependent energy losses anddelays of wires. The MRR approach minimize or eliminate the need for theinefficiency of multiple conversions between the electronic and opticaldomains as with previous solutions. IO power for flash buses today is˜10 pJ/bit and is a function of distance. Use of silicon photonics isexpected to reduce this by an order of magnitude.

In one implementation, an MRR based Silicon Photonics (SiPh)transceivers are integrated into the memory controller silicon as wellas the memory device multiplexer/driver silicon. Super-LuminescentDiodes (SLDs) provide multi-wavelength continuous wave (CW) light foreach transmitter. Single-mode fibers or optical waveguides embedded inthe PCB interconnect the controller silicon with the multiple expanders.Each single-mode fiber conducts DWDM (dense-wavelength divisionmultiplexing) signals in one direction (from transmitter to receiver).400 Gbps using 20 wavelengths around 1500 nm per fiber is feasible.Using low loss coupling methods between transceivers and PCB waveguideswould allow a single SLD to push data over multiple-drop receiverdevices.

FIG. 5 illustrates a communication network 500 using MRRs usingselective wavelength keying. Specifically, in FIG. 5 an incomingwaveguide 502 is configured to communicate optical signals over aplurality of wavelengths. A combination of a first MRR 504 and a secondMRR 506 is configured to alter the path of optical signals traveling onthe incoming waveguide 502 towards an outgoing waveguide 508. In oneimplementation, the first MRR 504 is configured to resonate at a firstwavelength λs_(1a) to direct a first component of an incoming opticalsignal towards the outgoing waveguide 508. Specifically, the resonantwavelength of the second MRR 506 is keyed down using charge carriermodulation of the second MRR 506 as the resonant wavelength of thesecond MRR 506 transitions from a first value to a second value, withthe first value and the second value being on opposite side of theresonant wavelength λs_(1a) of the first MRR 504. A heater A may heatthe first MRR 504 to key it to a given wavelength while heater B mayheat the second MRR 506 to key it to a different wavelength.

In one implementation, the resonant wavelength of the second MRR 506transitions from a first value to a second value in response to changein a heater power applied to the second MRR 506 as further illustratedbelow in FIG. 6. In an alternative implementation, the resonantwavelength of the second MRR 506 is keyed down using charge carriermodulation of the second MRR 506 by approximately 0.05 nm.

FIG. 6 illustrates a graph 600 illustrating relation between resonantwavelength of MRRs and heater power applied to the MRRs for selectivewavelength keying. Herein, a line 602 shows the actual wavelength as itis rapidly crossing between wavelengths λ₁ to λ₅ shown on a line 604. Aline 610 illustrates what the wavelength would be when the MRRs arekeyed with the charge carrier. As shown here, using the charge carrier,the system can key MRR down at 612 and let it follow the line 602 underλ2 and key it back up at 614. As the system can key the MRR down only inone direction, just before it hits λ3, the system can key the MRR downand then let it go and when it goes above λ3, I can go above it. A line620 illustrates how many mW of power is needed in to the heater for itto move the resonant wavelength.

FIG. 7 illustrates a communication network 700 with optical delay linesfor silicon photonics routing. For example, the communication network700 may have various data packets travelling over different wavelengthsλ_(l)-λ_(n). In one implementation of the communication network 700,each packet traveling on the communication network 700 has a first datacomponent (in some embodiments a header) including a second datacomponent (in some embodiments routing information). In oneimplementation, the header may be a predetermined number of bits or abarker code. Each packet traveling on the communication network 700 maytravel on its own wavelength. A drop filter (not shown) listens to thepackets being communicated over the communication network 700. When thedrop filter detects a header, it turns off the drop filter so that theremainder of the data packet continues on the communication network 700while the header is stripped using a silicon photonic component 702.

In one implementation, the silicon photonic component 702 may be an MRR.In an alternative implementation, the silicon photonic component 702 maybe a Mach-Zehnder Interferometer (MZI) SiPh component. The strippedheader is converted into electrical domain using a photodetector 704.Subsequently, the header is processed in the electrical domain using aheader detector 710 and the header detector 710 controls a router 708that redirects the data packet according the information from theheader. In some embodiments router 708 is an optical router.

The remainder of the data packet is communicated to an optical delayline 706. The optical delay line 706 delays the data packet in theoptical domain for a time period that may be necessary to process theheader in the electrical domain to obtain the routing information fromthe header and to set up appropriate routing switches on the router 708.In one implementation, the optical delay line 706 adds a delay ofapproximately 5 ns. The optical delay line 706 providing approximately 5ns of delay may be approximately 25 m in length.

Thus, the communication network 700 provides an optical fabric withswitching control information embedded in a header of optical packetstraveling on the communication network 700. The communication network700 uses the optical delay line 706 such that the header does not haveto be processed in the optical domain. On the other hand, it alsoensures that the data packet does not leave the optical domain. In oneimplementation, the data packet exiting from the optical delay line 706is communicated to the router 708 once one or more routing switches areset.

The above specification, examples, and data provide a completedescription of the structure and use of example embodiments of thedisclosed technology. Since many embodiments of the disclosed technologycan be made without departing from the spirit and scope of the disclosedtechnology, the disclosed technology resides in the claims hereinafterappended. Furthermore, structural features of the different embodimentsmay be combined in yet another embodiment without departing from therecited claims.

What is claimed is:
 1. An apparatus comprising: an incoming waveguideconfigured to communicate optical signals over a plurality ofwavelengths; and a combination of a first silicon photonics (SiPh)component and a second SiPh component configured to alter a path ofoptical signals traveling on the incoming waveguide towards an outgoingwaveguide, the first SiPh component configured to resonate at a resonantwavelength to direct a first component of an incoming optical signaltowards the outgoing waveguide, wherein a second wavelength (λs_(1b)) ofthe second SiPh component is adjusted down at a first value of thesecond wavelength (λs_(1b)) and is adjusted back up at a second value ofthe second wavelength (λs_(1b)) with the first value being lower thanthe resonant wavelength (λs_(1a)) of the first SiPh component.
 2. Theapparatus of claim 1, wherein a resonant wavelength of the second SiPhcomponent is adjusted down using charge carrier modulation of the secondSiPh component at the first value of the resonant wavelength of thesecond SiPh component and is adjusted back up at the second value of theresonant wavelength of the second SiPh component, with the first valuebeing lower than the resonant wavelength of the first SiPh component andthe second value being higher than the resonant wavelength of the firstSiPh component.
 3. The apparatus of claim 1, wherein the resonantwavelength of the second SiPh component is adjusted down, as ittransitions from a first value to a second value, in response to changein a heater power applied to the second SiPh component.
 4. The apparatusof claim 1, wherein the resonant wavelength of the second SiPh componentis adjusted down using charge carrier modulation of the second SiPhcomponent by approximately 0.05 nm.
 5. The apparatus of claim 1, whereinheater components are used to change the resonant frequencies of thefirst and second silicon photonics components.
 6. The apparatus of claim1, wherein at least one of the SiPh components is a ring resonator andthe incoming waveguide, outgoing waveguide, first SiPh component andsecond SiPh components are connected to storage devices via a network.7. The apparatus of claim 1, wherein at least one of the SiPh componentsis a micro ring resonator.
 8. A communication network comprising: aplurality of waveguides, each of the waveguides configured tocommunicate optical signals over a plurality of wavelengths; acombination of at least two silicon photonics (SiPh) componentsconfigured to alter a path of optical signals traveling on an incomingwaveguide towards an outgoing waveguide, a first SiPh componentconfigured to resonate at a first wavelength (λs_(1a)) to direct a firstcomponent of an incoming optical signal towards the outgoing waveguideand a second SiPh component configured to resonate at a secondwavelength (λs_(1b)) to direct a second component of the incomingoptical signal towards the outgoing waveguide, wherein the secondwavelength (λs_(1b)) is adjusted down at a first value of the secondwavelength (λs_(1b)) and is adjusted back up at a second value of thesecond wavelength (λs_(1b)) with the first value being lower than theresonant wavelength (λs_(1a)) of the first SiPh component and the secondvalue being higher than the resonant wavelength (λs_(1a)) of the firstSiPh component.
 9. The communication network of claim 8, wherein thefirst component comprises a header and the second component compriserouting information.
 10. The communication network of claim 8, furthercomprising a third SiPh component configured to resonate at a thirdwavelength (λs_(1c)) to direct a third component of the incoming signaltoward the outgoing waveguide.
 11. The apparatus of claim 1, wherein thefirst silicon photonics (SiPh) component is used to stripe a first datacomponent from a data packet.
 12. The apparatus of claim 11, furthercomprising one or more electrical domain components configured toprocess the first data component in an electrical domain.
 13. Theapparatus of claim 11, further comprising one or more router switchesconfigured to be set using a data packet output from processing thefirst data component in the electrical domain.
 14. The apparatus ofclaim 13, further comprising one or more optical delay lines configuredto generate data packets to be input to the one or more router switches.15. The apparatus of claim 14, wherein the optical delay line isapproximately 25 meters in length.